Fire tube hot water boiler



y 9. 1968 c. H. mm, 4 3,391,676

FIRE TUBE HOT WATER BOILER Filed April 17. 1967 CONTROL BURNER mvmon cmmuss H. Newman;

United States Patent 01 ice 3391,61 Patented July 9, 1968 3,391,676 FlRE TUBE HGT WATER BOILER Charles H. Neimnn, .Ir., York, Pa., assignor to York Shipley, Inc, York, Pa., a corporation of Delaware Filed Apr. 17, 1967, Ser. No. 631,265 5 Claims. (Cl. 122-406) ABSTRACT OF THE DISCLOSURE To prevent leakage between the tubes and tube sheet of a fire tube hot water boiler, a baflle plate is placed inwardly of and parallel to the hottest tube sheet. By an external piping and pump connection, boiler Water is positively circulated from the central portion of the boiler to the lower portion of the space defined by the baflle and tube sheet thus establishing a positive circulation of boiler water in immediate contact with the hottest portion of the tube sheet. Interlocking controls prevent firing of the burner until such positive circulation is established.

Background of the invention The present invention relates to fire tube boilers and more particularly to hot water fire tube boilers. Hot water fire tube boilers as distinguished from fire tube steam boilers have been very prone to develop leaks for reasons which are not easily susceptible of explanation. Suffice to say, such leaks do occur and for the reason that they do occur in spite of all prior attempts in the art to cure them, such equipment has fallen into some disfavor in spite of the fact that hot water heating systems are very much more desirable for a number of reasons than steam heating systems. While this problem is particularly acute in high pressure (e.g. 100 psi.) boilers, the problem is nevertheless present, although to a lesser degree, in low pressure (e.g. 30 psi.) boilers.

A number of methods of correcting this leakage problem have been tried by the principal manufacturers in this field over a number of years and to date nothing has been entirely satisfactory. Prior art attempts at solution to the problem included apparatus for preventing thermal shock in boilers of this kind through the use of a modulating valve in the water return line and apparatus of this type is shown in US. Patent No. 3,150,827, dated Sept. 29, 1964. Use of the modulated blending valve apparatus shown in that patent provided improved results but did not provide a complete answer to the problem. Others in this field have suggested increasing circulation in boilers of this type by so orienting the return line as to aid the normal thermal siphon circulation effect. An example may be found in the U3. patent to Gething 3,056,839 of 1962.

It is a well known fact that the boiling coefficient of heat transfer is substantially greater than the natural convection or even the forced convection coeificient of heat transfer. As the temperature of Water approaches the boiling point, the heat transfer coetficient increases over that at a lower temperature. This means that the coelficient of heat transfer continues to rise as the water is heated toward the boiling point. This may explain Why a low pressure hot water fire tube boiler, that is, one which operates at pressures of the order of 30 pounds per square inch or less, is less likely to leak than one which operates at pressures of the order of 100 pounds per square inch. To illustrate this point, assume a boiler which operates at 100 pounds per square inch pressure wherein the temperature is maintained at 220 F. The boiling point of water at 100 pounds per square inch is 338 F. and the difference between this boiling tempera ture and the water temperature in the boiler is 118".

Therefore the water temperature maintained in the boiler is substantially below the boiling temperature and consequently the heat transfer coetlicient would be lower than it would be in a boiler operated at 25 pounds per square inch and maintained at the same 220 F. temperature. The boiling temperature of water at a pressure of 25 pounds per square inch is 267 and the water is therefore only 47 below the boiling temperature. Since the water temperature in the 25 pound per square inch boiler is closer to the boiling temperature, the heat transfer coefficient would be closer to the boiling coefficient. This suggests therefore that in a steam boiler with a very high coefiicient of heat transfer, heat is rapidly taken away from the tube sheet and the tubes and therefore both should run cooler than they do in a hot water boiler where due to the lower coefficient of heat transfer, the heat is taken away less rapidly. Apparently it can also be assumed that heat is taken away less rapidly in a high pressure hot water boiler than it is in the low pressure hot water boiler.

Accordingly, it is the principal object of the present invention to improve the heat transfer coefficient between the water and the tube sheet and the fire tubes in a hot water fire tube boiler in order to eliminate insofar as possible any leakage in structures of this kind.

A further object of the present invention is to provide a positive circulation of water in immediate contact With the hottest portions of the hottest tube sheet.

Summary of the invention In general, the objects of the present invention are achieved as follows. A bafile member is placed within the boiler positioned inwardly of the hottest tube sheet and extending in substantially parallel relation thereto. This battle member in combination with the tube sheet therefore defines a relatively narrow space which is at least to some degree thermally isolated from the remainder of the boiler interior. \By external piping and pumping connections, boiler water from a point remote from the rear tube sheet is circulated through such piping and directed upwardly into the space between the baffle member and the tube sheet which establishes a positive circulation of boiler water in intimate contact with the hottest portions of the tube sheet. An interlocking control arrangement is also provided which prevents firing of the burner unless positive circulation has been established in that area between the baffle and the rear tube sheet.

Brief description of the drawings FIGURE 1 is a side elevation partly in section of a fire tube boiler showing the bafile member adjacent the rear tube sheet;

FIGURE 2 is a section on the lines 22 of FIGURE 1;

FIGURE 3 is a plan view of the baffle member proper;

FIGURE 4 is a section on the lines 44 of FIGURE 3; and

FIGURE 5 is a schematic wiring diagram showing the interconnection of a flow switch in series with the main burner controls.

Detailed description of the drawings Referring first to FIGURE 1 which shows a side elevation partly in section of a fire tube boiler embodying the apparatus of the present invention, the boiler shell is indicated by the reference numeral Ill. Housed within the shell 16 in an entirely conventional manner are a plurality of fire tubes 12 supported between front and rear tube sheets 14 and 16, respectively. The burner, which is not shown on the drawing, would be positioned to fire into the combustion tube 13 at the left hand side of FIGURE 1 and the combustion products would proceed from left to right in this figure. Upon reaching the end of the combustion tube 18, the combustion products would be returned through the fire tubes 12 to the left hand end of the boiler and then out the stack coupling at the right hand end of the boiler. Thus far, the apparatus is entirely conventional.

The bafile plate which is one element of the combination of the present invention is designated by the reference numeral 22 and is shown in plan view in FIGURE 3. The openings in the baffie plate which accommodate the fire tubes are just slightly larger in diameter than the outside diameter of the tubes to restrict the flow of water in the annular space between each tube and the baifie. FIGURE 1 shows the positioning of the baffie plate within the boiler 10. It will be noted that it is spaced inwardly a small distance from the rear tube sheet 16 and extends in generally parallel relation thereto. As thus positioned, a confined water circulating space is defined by the baflle 22 and the rear tube sheet 16. At the lowermost portion of the boiler, the baffie plate is stepped inwardly as shown at 24 in order to accommodate attachment of a fitting 26 which fitting communicates with the space between the bafile plate and the rear tube sheet. On the face of the baffle 22 which faces the tube sheet, there are mounted a plurality of small baffie members 23 adjacent the lower edge of the bafile 2.2. The purpose of these members is to insure circulation of water vertically along the face of the tube sheet and around the ends of the fire tubes rather than along the path of least resistance which would be between the shell and the tubes. A piping connection generally indicated at 28 connects the fitting 26 to a second fitting 30 which is preferably positioned somewhere on the center line of the boiler and at a point remote from the location of the bafiie plate 22. Connected into the piping 28 is a circulating pump 32 and a flow switch 34. As shown in the schematic wiring diagram in FIGURE 5, the flow switch 34 is placed in series with the main burner control to prevent firing of the burner until positive circulation has been established by the pump 32.

It is believed that the operation of the aforedescribed apparatus will be apparent to those skilled in the art. The pump 32 is effective to establish a positive circulation of boiler water through the narrow space defined by the baffle member 22 and the rear tube sheet 16.

Apparatus in accordance with this invention has been actually installed and operated for a period of several months. The particular boiler on which this apparatus was installed included a blending valve of the type shown in U.S. Patent 3,150,827 and yet had a long history of leakage and none of the prior attempts to correct the leakage were entirely successful. Several months after the installation of the apparatus of the present invention, however, the boiler was opened and found to be completely free of leakage. The exact reason for the successful operation of this apparatus is not entirely known. It is assumed, however, that by providing a positive circulation of water adjacent the hottest portions of the tube sheet where leakage had previously occurred, that the rate of heat transfer from the tubes and the tube sheet to the boiler water was increased by an amount sufficient to prevent thermal dimensional changes which otherwise would have resulted in leakage.

The invention has been described with reference to a three pass scotch boiler but no limitation of the scope of the invention is intended thereby. The bafile plate should always be positioned adjacent the hottest tube sheet regardless of the type of boiler and that tube sheet is always the one where the combustion gases first enter the fire tubes. 1

While a preferred embodiment of the present invention has been herein shown and described, applicant claims the benefit of a full range of equivalents within the scope of the appended claims.

I claim:

1. A hot water fire tube boiler comprising in combination:

an outer shell housing the fire tubes and forming a storage vessel for the water to be heated;

front and rear tube sheets supported within said shell and supporting the fire tubes therebetween;

a baffie plate positioned substantially parallel to and spaced inwardly from that one of said tube sheets where combustion products first enter the fire tubes, said baflie defining with said tube sheet a water circulating path; and

means external to said boiler connected with said water circulating path and a remote portion of said boiler for effecting a positive circulation of water from said remote point through said water circulating path and back to said boiler.

Z. The combination defined by claim 1 including means for preventing the firing of the burner in the absence of positive circulation of water through said water circulating space.

3. The combination defined by claim 1 in which said last-mentioned means comprising piping external to and communicating with the interior of said boiler, extending from a point on the side thereof to a point at the lower end of said baffie and rear tube sheet and a pump connected in said piping.

4. The combination defined by claim 1 in which said bafiie plate includes along the lower edge thereof, a plurality of battle members extending between said plate and said tube sheet to direct circulation of water vertically along the face of said tube sheet and over said fire tubes.

5. A horizontal hot water fire tube boiler comprising in combination:

an outer shell housing the fire tubes and forming a storage vessel for the water to be heated;

front and rear tube sheets supporting the fire tubes and positioned within said boiler;

a baflie member positioned substantially parallel to and spaced inwardly from that one of said tube sheets where combustion products first enter the fire tubes, said baffle member overlying approximately onehalf the area of said one tube sheet;

piping means communicating with the space between said baffle member and tube sheet at the lowermost extremity thereof, said piping means also communieating with the interior of said boiler at a point remote from the location of said bafile member;

a pump connected in said piping;

a flow switch connected in said piping; and

means for preventing firing of the burner until said fiow switch has been activated corresponding to positive circulation of boiler water through the space defined by said baffle member and rear tube sheet.

References Cited UNITED STATES PATENTS 2,189,443 2/ 1940 Brantly 122-406 FOREIGN PATENTS 738,205 7/1966 Canada.

KENNETH W. SPRAGUE, Primary Examiner. 

